The Unknown Side Effect
by SeeMeSoar
Summary: Clint and Natasha's children join the crowd of crazy people at Stark Tower. Jacob Peter Barton is his mom's boy. Sarah Lila Barton is her dad's girl. But love of archery isn't the only thing Sarah picked up. She also picked up exposure to the tesseract. I don't own the Avengers.
1. Chapter 1

**Disclaimer: I don't own the Avengers.**

Neither Clint or Natasha knew what was going to happen. Honestly, the fact that Natasha could even become pregnant surprised them both. But, nine months later, Natasha lay in a hospital bed smiling at the two balls of love in her and her husband's arms. No one else was in the hospital room but the small family. The baby girl in Clint's arms was awake and moving, messing with the strap of his arrows. Luckily, none fell out. The little boy snuggled against Natasha's body and slept, letting out little snores. "He sounds like you do, Clint."

"I do not snore," Clint protested.

"You do," Natasha told him.

There was a small knock at the door. "Come on in," Clint said, grateful for the change of topic.

Maybe he should have pretended he didn't hear and Natasha was asleep. The team of Avengers, along with Jane, Pepper, and Darcy, all walk into the room. "You didn't tell us they were twins!" Tony said, grinning.

"You should have asked Jarvis, Steve, or even Pepper."

"You told my wife but not me?"

Natasha smiled impishly. "So what are the names?" Pepper asked.

"We haven't decided yet."

"Wait right here." With a dash, Pepper flew out of the room. In five minutes she was back with a small book under her arm.

"Is that what I think it is?" Natasha asked. Pepper nodded. Handing the book to Natasha, Pepper stepped back to let the couple pick names. The two flipped pages, scanning names, until they saw two names. Four, if you count the ones below it. The couple whispered until they stopped.

"We have names," Clint said.

"Sarah Lila Barton and Jacob Peter Barton."


	2. Chapter 2

**I don't own the Avengers.**

Clint sat in the twins' room, playing with his daughter. Sarah was cooing, patting his cheek, and giggling. Sarah's normally brown eyes turned blue and she started shaking. In less then a minute, her eyes were back to normal, but she was crying. "I've got you," Clint told her, hugging his small daughter to his chest. He had known the shade of blue that took over her eyes very well. Tesseract blue.

The next day, he got up early. Knowing Thor normally spent this hour at the top of the tower, he stepped into the elevator. "High up as you can go, please. And don't tell Natasha anything."

"Yes sir." Within a few minutes, he was talking with Thor.

"Thor, I need to talk to Loki."

"Loki? Why?"

"Because I think something's happening to my daughter because of the Tesseract."

"Very well. Does Lady Natasha know of this decision?"

"No. She has no idea about any of this, Thor."

And he would keep it that way. He had brought this problem against his daughter, and he would fix it.

Halfway through the day, Natasha cornered him. "I know what you said to Thor."

"What?"

"You know perfectly well how lightly both of us sleep. I just followed you until I figured out what was going on."

"You weren't supposed to know."

"Why? It is our kid, Clint. I would do anything for her."

She hugged him. Leaning into his chest, she whispered, "That cube has ripped us apart. It won't rip our daughter apart either."

"I know it won't." They stayed there for a moment, pressed against each other, until the wailing sounds of Jacob from the twins' nursery pierced their way through the hallway. As Clint rocked The baby back and forth in his arms, he smiled at him. Jacob oohed and grabbed his chin.

"You got quite a grip, little guy," he said.

"He got it from you two, course it is. Your kids are going to be ninjas," Tony joked from the doorway. "I have a couple of presents for the little kids."

From behind his back, he pulled out four bags. The first thing he pulled out was a stuffed dog. Black, grey, and white, the little eyes beamed at the room-one blue, one brown. A blue collar graced the dog's neck. The second thing was a grey and brown puppy with green eyes and a orange collar. At the sight, Jacob made grabbing motions at the second dog. Picking it up, Tony set it gently in the little boy's arms. Jacob hugged it tight to his chest. Next, Tony pulled out two mobiles. Four stuffed dolls dangle off them. In the center, four faces smile down at the floor. The four faces are Natasha, Clint, Jacob, and Sarah. The dolls are the Hulk, Thor, Iron Man, and Captain America. "Tony," Natasha said. "They're beautiful."

Tony fastened the two mobiles onto the two cribs before moving on to the last presents. Two little hats, one blue and one orange, were gently placed on the dresser. Both had little birds sewn into the designs. Little spider webs separated each bird from the next. Tony smiled. "I may have had some say about the designs on the hats."

"Tony, all of it is so amazing," Natasha said. "Thank you."

"Friend Clint?" Thor said, moving into the room. Noticing that Natasha was in the room, he stopped.

"It's alright, Thor," Clint told him. "She figured it out."

"I am not surprised. Lady Natasha is quite clever. Well, I've arranged transport to Asgard for you. Would you like to come along, Lady Natasha?"

"If it isn't too much trouble."

"It is not."

"Wait, why are you going to Asgard?" Tony burst out.

"Loki gave Sarah a little present," Natasha said, growling.

It was time to visit the trickster.


	3. Chapter 3

**I don't own the Avengers.**

Clint is done with security. Beyond done. Sure, Loki was dangerous. Sure, they couldn't let just everyone in. But Clint's daughter could be in danger. He didn't care a bit about the security. Luckily, they let the duo through. Thor, being Prince of Asgard and everything, gets to skip the line, something that Clint would love. Thor leads them to the cell. He pushes the door open and the three slip in, closing the door behind them. Loki looks up. "Brother, Barton, Romanoff."

"It's just Barton now," Natasha said.

"My congratulations. Why are you have you come? I doubt you wanted to give me company."

"You first hit me with the Tesseract. You're the expert on it. My daughter is being attacked from the inside out by that thing. I want to know how to get it out of her."

Loki laughed. "There's nothing funny about this at all," Natasha said.

"Tell me about the child. It always matters when it comes to them. Do you two have any other children?"

"Jacob."

"Older brother, younger brother, what?"

"Twins. Sarah's older."

"Has Jacob shown anything similar to Sarah?"

"No."

And back and forth they went. Loki would throw out a question. Clint or Natasha would answer it. Eventually, Loki ran out of questions. "Well, I can't be sure, but I know that your child is going to be pretty powerful. Also, if anyone touches her and she doesn't like it, the Tesseract's going to react. Badly. Be careful who's watching her."

"What do you mean, powerful?"

"More power than Stark could dream of having in his metal suit."

Natasha raised her eyebrows. "We aren't here because we want to know how powerful she is. Is the Tesseract going to harm her?"

A pin could have dropped and any of the people in the cell could have heard it. Loki thought about it. "Socially, almost definitely. Mentally, possibly. And physically, no one could ever harm her because of it."

"Define socially and mentally."

"Socially- well, let's say someone pushes her. If she doesn't like that, the Tesseract will flare up. That will not bode well among anyone. Mentally- well, that we have yet to see." He turns away, ending the conversation. Thor escorts the duo out of the cell and back to the Bifrost, sending them back to Stark Tower.


	4. Chapter 4

**I Don't Own The Avengers.**

_The twins are about five years old._

It was recess at the twins' school. Flurries of small children flocked around the playground. From the swings, several kids were engaging in the daily contest. One would fly off at the highest point on the swing's arch, another would take his or her place and start swinging. Sarah leaned off the playground structure to watch. Jacob was waiting in line. When he finally got to compete, he pulled himself into the seat and swung wildly. He got to the height of the arch and jumped off, rather awkwardly. As he soared through the sky, he crumpled on impact. He looked up, revealing two knees scraped badly. At the sight of her brother's tears, Sarah was quickly down on ground. Leaping off the slide, she was quickly by her brother's side. One of the other boys sneered at the two. "What a baby! Only babies cry."

"My brother is not a baby," Sarah insisted.

"Definitely a baby. His sister has to stand up for him."

Sarah took a step towards the boy. "My brother is not a baby."

"Oh yeah? I bet your brother is weak."

"My brother is not weak, and he is not a baby." With that, she took another step. The two stepped towards each other, still arguing, until Sarah grew annoyed and moved towards the boy in an unmistakable fist. Noticing the girl's move, the boy hit her first. As soon as his fist collided with her shoulder, a blue sphere threw itself around Sarah, knocking the boy out of her way.

"Freak! A girl freak and a boy baby! A couple of nerds and lame-os!" the boy screamed. As the sphere disappeared, Sarah curled up into a ball. From the area where the teachers were, four of them moved. One surged to the office, another one went to the boy's side, one headed for Sarah, and the fourth sat down with Jacob.

Sarah crawled over to Jacob. The teacher was wiping the scrapes down. Jacob had stopped crying, but he had soaked his cheeks so much no one could tell. "We've called your parents to come pick you up," the teacher told him. "They'll be here soon."

As soon as they saw their parents, they ran for the car that had pulled in. Happy was waiting for them and drove to the reconstructed Stark Tower. Once there, Tony used the TV to pull up a little kids' show. Sarah snuggled into the sofa, almost to the point where no one could see her. Jacob sat in Natasha's lap, who was leaning into Clint. Eventually all the Avengers flocked into the room. Steve was looking at papers that Fury had gave him. Thor was eating poptarts, his favorite Midgardian food. Tony was talking to Pepper, and Bruce was sitting on the couch, tickling Sarah's stomach, making her giggle like mad. And as Sarah's giggles echoed through the otherwise empty tower, all of them were happy.


End file.
